End mills are tools which are configured to be coupled to a rotating drive of a milling machine for utilization in cutting a work piece with the milling machine. End mills come in a variety of different configurations depending on the material to be cut and other factors such as the shape of cut to be made and whether the work piece is to be rough cut or cut to precise finish dimensions.
Typical end mills have a generally cylindrical form with a shank at one end adapted to be attached to the rotating support of the milling machine and a tip opposite the shank. A series of flutes are cut helically from the tip of the end mill to a midpoint of the end mill where the shank begins. Between the flutes cutting teeth are provided. These teeth have a sharpened cutting edge on a leading side thereof and a heel on a trailing side thereof. Typically, a land exists between the cutting edge and the heel.
This cutting edge of each tooth acts to cut into the work piece when the end mill is traveling laterally and spinning. The tip of the end mill also typically includes sharpened tip cutting edges so that the end mill can also cut the work piece when the end mill is moving axially into the work piece. The specific contours of the tip and cutting edges of the end mill can be configured in many different ways depending on the particular material to be cut and other desired performance characteristics. For instance, the helical angle of the flutes and teeth can vary, the number of flutes and teeth can vary, and other factors such as a degree of radial rake, the degree of relief behind the cutting edge, and particular geometry of the end cutting edges including the various clearance angles, dish angles, axial rake angle, and gash angle can all be particularly selected based on the desired performance for the particular end mill.
One factor influencing the quality of cut made by an end mill on a work piece is the presence of vibration. Vibration between the end mill and work piece can cause the end mill to become prematurely worn or broken, can require slowing of the milling operation, can result in off tolerance cutting of the work piece, as well as other potentially undesirable consequences. Vibration frequencies and amplitude are controlled by many different factors including the rate at which the end mill is spinning, the rate at which the end mill is translating, both laterally and axially, the size of the end mill (i.e. the diameter) and the number of teeth on the end mill. Also, the material from which the end mill is formed and the material making up the work piece can influence the frequency and amplitude of vibration, as well as other factors.
It is known in the prior art to minimize such undesirable vibration by contouring the cutting edges of the teeth on the end mill to undulate. These cutting edges are typically provided in a sinusoidal undulating pattern from the tip to the root of each tooth along the land surface between the cutting edge and the heel of each tooth. This contouring also tends to decrease the chip size produced when the end mill cuts the work piece. With the chip sizes being somewhat randomized and decreased in size, the potential for vibration is minimized. These prior art end mills are referred to as roughing end mills because they do not provide a smooth finish cut.
Such roughing end mills can be passed more quickly through the work piece than finish end mills, without as great of concern for vibration. However, roughing end mills are not typically sufficient when a smooth and precise finish contour for the work piece is required. Rather, the roughing end mill leaves the cut surfaces of the work piece rough in form. One attempt to combine the low vibration attributes of a roughing end mill with the smooth and precise finish of an unnotched end mill has been disclosed by Iscar Metals, Inc. of Arlington, Tex. One such combination roughing and finishing end mill is marketed by Iscar Metals, Inc. under the trademark “FINISHRED.” With this prior art end mill, some of the teeth have an undulating sinusoidal cutting edge. Other cutting teeth have a smooth cutting edge. The smooth cutting edge and undulating cutting edge are provided in an alternating pattern. While such a combination roughing and finishing end mill exhibits a degree of effectiveness in reducing vibration and improving finish appearance of the work piece, the results are not entirely satisfactory. Rather, some vibration still is provided and the surface of the work piece is typically not as smooth as would be the case with a smooth cutting edge finishing end mill. Also, such an alternating undulating and smooth cutting edge end mill is only possible when an even number of teeth are provided on the end mill. Many end mills beneficially have an odd number of teeth (i.e. three or five, etc.) and so cannot have such an alternating pattern without some discontinuity in the pattern.
Accordingly, a need exists for an end mill which can very quickly and very precisely cut through a work piece with minimal vibration. Such an end mill is disclosed hereinbelow.